(a) Technical Field
The present invention relates to a catalyst that can be used in a process of preparing 1,3-butadiene, and particularly to a multi-component Bi/Mo/Fe-based oxide catalyst, which is prepared by co-precipitation in a pH-adjusted solution and shows superior selectivity towards 1,3-butadiene using n-butene (1-, 2-, iso-butene), while exhibiting a relatively slow deactivation. The present invention also relates to a process of preparing the catalyst. A process of 1,3-butadiene using the catalyst is also disclosed in the present invention.
(b) Background Art
Lower olefins such as ethylene, propylene, butene and butadiene have been used as raw materials of polyolefins and the starting materials for various chemicals in the petrochemical industry. Although the thermal cracking of naphtha is still a major process for the production of lower olefins, various processes such as the thermal cracking of ethane and fluid catalyst cracking produce the lower olefins as supplementary process. However, the thermal cracking has become important as supplementary production process of the lower olefins. The high temperature operation of the thermal cracking process inevitably requires a large amount of energy. However, it is widely used because of the simplicity and convenience in process operation. However, the construction of new naphtha cracker becomes difficult because naphtha cracking produces side products other than butadiene and production cost increases considerably due to the increase in the cost of naphtha and energy.
Another method of preparing butadiene is a direct hydrogenation of n-butene. This is an endothermal reaction requiring much energy, and forms coke on the surface of a catalyst thus decreasing the activity of the catalyst. Various attempts have been made to overcome these drawbacks.
It is possible to obtain butadiene by oxidative dehydrogenation (ODH) of n-butene. ODH is an exothermal reaction and can be conducted at a relatively low temperature, thereby reducing the amount of energy consumption. This is also advantageous in that it can prevent the production of coke and also the presence of oxygen results in significant decrease of cracking and formation of coke. Examples of the conventional oxidants include oxygen, sulfur compounds, carbon dioxide and steam [M. A. Botavina, G. Martra, Yu. A. Agafonov, N. A. Gaidai, N. V. Nekrasov, D. V. Trushin, S. Coluccia and A. L. Lapidus, Appl. Catal. A: Gen., 347, 126 (2008)].
Various metal oxides are used as catalysts in the ODH of butene [E. J. Miklas, U.S. Pat. No. 3,937,748 (1976), H. H. Kung, B. Kundalkar, M. C. Kung and W. H. Cheng, J. Phys. Chem., 84, 382 (1980), M. Misono, K. Sakata, F. Ueda, Y. Nozawa and Y. Yoneda, Bull. Chem. Soc. Jpn., 53, 648 (1980), B. L. Yang, F. Hong and H. H. Kung, J. Phys. Chem., 88, 2531 (1984), V. V. Krishnan and S. L. Suib, J. Catal., 184, 305 (1999), J. A. Toledo-Antonio, N. Nava, M. Martinez and X. Bokhimi, Appl. Catal. A: Gen., 234, 137 (2002). In particular, Bi Mo complex oxide catalyst, a complex of Bi oxide and Mo oxide, has been reported as having superior catalytic activity [M. Niwa and Y. Murakami, J. Catal., 27, 26 (1972); W. J. Linn and A. W. Sleight, J. Catal., 41, 134 (1976); A. P. V. Soares, L. D. Dimitrov, M. C.-R. Andre de Oliveria, L. Hilaire, M. F. Portela and R. K. Grasselli, Appl. Catal. A: Gen., 253, 191 (2003)].
In the ODH of n-butene, n-butene binds to Mo6+ ions, and electrons produced in the binding reduce other Mo6+ ions to provide Mo5+ ions. The produced Mo5+ ions react with Bi3+ ions and Mo6+ ions are regenerated. The reduced Bi2+ ions are oxidized again after the reaction with oxygen. Contents of Bi and Mo are very important because Bi Mo catalyst experiences such an oxidation-reduction mechanism.
According to the molar ratio of Bi and Mo and the catalyst manufacture conditions, Bi Mo oxide catalysts are classified into α-phase (Bi2O33MoO3), β-phase (Bi2O32MoO3) and γ-phase (Bi2O3MoO3). The β-phase and the γ-phase Bi molybdate catalyst have been reported as having superior catalytic activity [H. H. Voge and C. R. Adams, Adv. Catal. Related Sub., 17, 151 (1967)]. Korean patent No. 10-0847206 discloses that iron ferrite is a superior catalyst for the preparation of 1,3-butadiene. Korean patent publication No. 10-2007-0103219 discloses a Bi molybdate catalyst, its preparation method and a process of preparing 1,3-butadiene by using the catalyst.
The ODH of butene is conducted at the temperature of 400° C. or higher. Moreover, water is supplied as a reactant and also produced during the reaction. This requires the hydrothermal stability of catalyst and the mechanical stability against the valence change of metal. On the other hand, if the number of active site on catalyst surface is too large, allyl intermediate is polymerized and coke production causes a relatively fast deactivation. When the number of active site is too small, conversion and yield of 1,3-butadiene (1,3-BD yield) can be lowered. Consequently, the active material which increases the mechanical strength and catalytic activity is necessary. Catalytic activity can be maintained and 1,3-BD yield can be improved when electron migration between complex oxides is facilitated and oxidation-reduction is thus promoted.
Bi Mo oxide was considered as a preferable catalyst in the conventional process of preparing 1,3-butadiene. However, despite its relatively high reaction activity and 1,3-BD yield, the Bi Mo (BM) catalyst changes into various phases and significantly varies in activity depending on the synthesis conditions and Bi Mo contents. In particular, although β-Bi Mo having a Bi/Mo molar ratio of 1 shows the highest activity, it disadvantageously changes into various phases at a particular temperature or higher. It also causes mechanical fatigue depending on the change in the valence during the reaction, thus lowering catalytic properties.